1. Field of the Invention
The present invention relates to g-hardened flow control systems and more specifically to flow control systems for grenade or mortar rounds fired out of short barrels necessitating very high firing or launch accelerations. The present invention further relates to grenade and mortar round flow control systems that act to improve the rounds' range and precision. The present invention further relates to a method of operating such a flow control system.
2. Technology Review
Short-barrel munitions, such as grenades and certain size mortars, experience high accelerations or setback loads during their firing or launch as a result of their having to reach their final launch velocity within a short amount of time. This firing or launch acceleration can be on the order of tens of thousands of g's, where one g is approximately equal to 9.80665 meters per second per second. For the purposes of this application, a “short barrel” is one of length between 9 inches to 12 inches when used to fire 40 mm grenades.
Traditional munitions of the type fired out of short-barrel guns are propelled by the ignition of powder charges which combust quickly inside the barrel, and such munitions are stabilized only by passive tail fins. Unlike rockets, which have continuous propulsion throughout flight, traditional munitions have a range limited by the charge combustion energy expended in the instant of firing, and unlike guided missile systems, have an accuracy and precision determined principally by the aim of the launch barrel, wind and air conditions, and whatever variations and imbalances may exist in the munition round. Range limitations, aim error and random or biasing disturbances may thus cause an unguided munition to be incapable of reaching a target or may require many rounds to strike suitably nearby the target owing to the large circular error probable (CEP), a measure of munition precision defined as the radius within which 50% of correctly aimed rounds may fall. Aside from the obviously undesirable outcome of missing an intended target, a round having insufficient range and/or CEP may inflict collateral damage which is also highly undesirable, particularly in urban warfare scenarios, and may put at risk the mortar firing crew for the duration of whatever excess time is needed to fire the increased number of rounds required for target saturation. By contrast, range extension and CEP enhancement permits the use of fewer rounds, directly translating into lowered logistical costs, speedier engagement resolutions and improved mission outcomes.
What is needed is a system that would increase both the effective range and the CEP of munition rounds fired from short barrels, without deviating from the caliber and general form factor of these traditional rounds so as not to obsolete standard issue mortars and grenade launchers. It is an object of the present invention to provide a system with one or more of these advantages over traditional grenades and mortar rounds.
The recent trend in gun-fired munitions development has been add guidance capability to small- and medium-caliber mortar rounds without directly addressing range limitations. The XM395 Precision Guided Mortar Munition (PGMM), a 120 mm guided mortar round produced by Alliant Techsystems (ATK), uses fixed canards mounted to a rotating nose spun counter to the spin of the round body (which is made to spin by means of canted tail fin extensions) to direct the mortar round in flight and correct its course to a target. A similar design mortar round by BAE Systems and General Dynamics Ordnance and Tactical Systems (GD-OTS), the 81 mm or 120 mm Roll Controlled Guided Mortar (RCGM), uses curved or airfoil-shaped canards on a collar that is spun counter to the spin of the round body (which, again, is made to spin by means of canted tail fin extensions) to direct the mortar round in flight and correct its course to a target. ATK's rounds have reportedly demonstrated a CEP of less than 10 meters at ranges in excess of 6,500 meters while rounds using the BAE/GD-OTS approach reportedly achieved an average miss distance of roughly 7 meters at ranges between 980 and 4,000 meters in firing tests done in 2012.
These experimental technologies have been very promising but still have the drawback of inherent limited range of the mortar round to the distance that can be achieved of an ordinary ballistic path given the velocity of the round at the time of gun expulsion. Range can be improved with these approaches by use of greater amounts of firing charge but even this is limited both by the spatial volume available for charge packages and by the amount of acceleration (setback load) the round can tolerate on firing given the g-force sensitivity of its sensor, processor, and braking components.
Additionally, the technologies currently being developed for mortar rounds have limited applicability to smaller rounds such as fired grenades.
What is needed is a system capable of providing both extended range and enhanced precision to gun-fired munitions. What is also needed is a system capable of providing reduced circular error probable (CEP), enabling a target to be effectively attacked with fewer rounds. What is also needed is a technology which could be applicable to high-g munitions of various calibers and sizes, including mortar rounds and grenades. What is also needed is a system capable of providing a larger maneuver footprint for fin-stabilized munitions of every caliber. It is an object of the present invention to provide a system with one or more of these advantages over the traditional systems and the systems described above.
Achieving these goals in a guided munition round inherently adds cost to the round. Whatever approach is taken, it cannot be ultimately more expensive than traditional approaches, all costs accounted for. Naturally, the externalities of collateral damage caused by inaccurate unguided munitions should be factored into the economic analysis, but preferably, the improvements made in a guided munition do not add so much cost to the munition as to make them prohibitively expensive, or even more expensive overall than unguided munitions even without the costs of externalities accounted for. The improved munition should also be as simple to use and as low-waste as possible.
What is needed, therefore, is a system capable of extending range and enhancing precision of high-g munitions in a sufficiently low-cost manner such that the new range and precision capabilities of the weapon more than compensate for the additional cost of the round, without the use of complicated and wasteful sabots. The present invention achieves these goals by making innovative use of both traditional and novel control technologies.